Radiofrequency amplifying system



July 15, .1930. F. H. MACKENZIE 1,770,541 v 'RADIOFREQUENCY AMPLIFYING SYSTEM Original Filed Aug. 1, 1325 ll it l FRANKLIN H. MACKENZIE, OF BYWOOD, PENNSYLVANIA.

RADIOFREQUENCY AMPLIFYING SYSTEM Application filed August 1, 1925, Serial No. 47,516. Renewed January 6, 1930.

My invention relates to radio receiving apmultiplicity of circuits, and a single circuit paratus. is, therefore, described 1n detail. The figure The object of the invention is to provlde a shows a reflex circuit comprising an antenna 1 receiving circuit having a number of stages connected tothe ground at 26 through induc- I; of radio frequency amplification wherein t ance 2. In inductive relation to coil 2 is an 55 certain elements of the tuning devices may be other inductance 3 connected in parallel with caused to produce a regenerative or reed-back variable condenser 1, elements 3 and a ointly effect, from stage to stage; that is, the teedconstituting a tuned circuit connected to the back takes place not between the elements oi grid 21 or" audion 5 and grounded through the z a single audion, but between coils in the cirsecondary winding of transformer 7 to 60 cuits of the several tubes. This is accomground 26. The filament 20 of this audion is plished, say in two-tube receiving set, by roenergized by the usual battery A, a rheostat 9 tating the coil or coils of the central tuned being interposed in the negative lead, as circuit until the maximum permissible feedshown.

15 back occurs between it and the two outer coils. The-positive terminal of the high-voltage 65 This circuit is characterized by a peculiar battery B is connected to the plate 22 of this roaring sound, on both sides of which a poaudion through coil 12 and the primary of sition of clear reception is located, instead of transformer 8. A protective resistance 10 is having a zone of clear reception between two connected between the positive terminal of :3 zones of roarin (or whistling) as in the ordithe A-bat-tery and the negative terminal of 70 nary regenerative circuit. I believe this roar the B-battery, as shown. This may be of the in my set is due to the successive beat notes of character disclosed and claimed in the cothe two tubes, not the self oscillation of a sinpending application, Serial No. 690,169, filed gle tube. February 2, 1924.

33 Broadly stated the invention comprises a Coil 13 is placed in inductive relation to method oi operating a radio frequency :11 1- coil 12, and is connected in parallel with the piifying system, which system comprises at variable condenser 14, as shown. This coinleast three tuned radio frequency transformbinatlon constitutes a tuned circuit which is ers interconnecting thermionic devices, one of connected to the negative terminal of the said transformers being adjustable *ith refbattery A through the secondary winding of \v erencet-o the other two, and the improvement transformer 8, and to the grid 2% of audion 6. in the method comprising adjusting the one The filament 23 of said audion is energized transformer with reference to the other two by battery A, as shown, a rheostat 11 being so that the maximum useful feed back of eninterposed in the negative side of the circuit.

:15 erg occurs between the adjustable transtorm- The positive terminal of battery B is con 0 er and the other two, and regulating the sysnected to the plate 25 of the audion by a cirtem in such a manner that substantially no cuit including the telephone receivers 18 and self-oscillation occurs in the thermionic deinductance 15 in series. vices. Coil 15 is inductively related to coil 16,

A clearer understanding of the invention which, in parallel with variable condenser will he obtained from the following specifica- 17, constitutes a tuned circuit. This circuit tion and the drawing accompanying the same. is connected to the primary winding of trans- In said drawing: former 7, a crystal detector or other rectify- The figure represents a reflex circuit of ing means 19 being interposed in series in otherwise well known type, but modified to said connections. embody my invention. In operation, the incoming radio frequency While it is, of course, obvious that my incurrents are passed from the antenna coil 2 vention may be applied to any circuit em to grid 21 by means of the tuned radio freploying several stages of radio frequency amquency circuit 3, 1; are amplified by audion 5 10) plification, it is unnecessary to illustrate said and passed on to audion 6 by coil 12 and tuned radio frequency circuit 13, 14 to the grid 24. The audion 6 feeds the further amplified currents from coil 15 to the tuned radio frequency circuit 16, 17, whence they 6 pass through rectifier 19 into the primary of transformer 7, as shown. Because of the action of rectifier 19, however, the impulses have now become unidirectional impulses of audio frequency which produce audio frem quency alternating circuits in the secondary of transformer 7. These audio frequency circuits are passed to grid 21, and amplified currents of similar nature are produced in the output circuit which pass into the trans- 15 former 8 and thence to grid 24. After further amplification by audion 6, the currents produce corresponding sounds in the telephone 18.

The desired maximum useful feed back 20 action may be obtained by turning the center coil 12 or coils 12. 13, so that its turns are at or nearly at right angles to the end coils. The outer or end coils are then turned to resonance, and a roar is produced, leaving the center coil at or nearly at the right angle position, and turning the end coils slightly out of resonance. This results in bringing in the signals with decidedly better amplification than other radio frequency circuits. It is found that by operating in this manner, a point may be reached where self-oscillation of the tubes or thermionic devices is substantially eliminated.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is: p The method of operating a radio frequency amplifying system, which system comprises at least three tuned radio frequency transformers interconnecting thermionic devices, one of said transformers being adjustable with reference to the other two, the improved method comprising adjusting the one transformer with reference to the other two so that maximum useful feed back of energy occurs between the said adjustable transformers and the other two and regulating the system in such a manner that substantially no self-oscillation occurs in the thermionic devices.

In testimony whereof I affix my signature.

FRANKLIN H. MACKENZIE. 

